Field of the Invention
The present invention relates to a low-pressure-loop exhaust gas recirculation apparatus of an engine, provided in a supercharger-equipped engine and configured to allow part of exhaust gas discharged from the engine to an exhaust passage to flow as exhaust recirculation gas into an intake passage to return to the engine.
Related Art
There is conventionally known that an engine equipped with a supercharger is provided with an exhaust gas recirculation (EGR) apparatus. JP-A-2012-229679 discloses an engine provided with a supercharger of the above type and a low-pressure-loop EGR apparatus provided in the engine. This supercharger includes a turbine provided in an exhaust passage and a compressor provided in an intake passage and driven by the turbine. This EGR apparatus is provided with an EGR passage between the exhaust passage downstream of the turbine and the intake passage upstream of the compressor, and an EGR valve in the EGR passage. This EGR apparatus is configured to respond to a strict demand for reduction of NOx and to restrict a returning amount of EGR gas by closing the EGR valve as needed in order to prevent corrosion due to condensed water generated in the EGR passage.
Herein, when a pressure difference between an inlet and an outlet of the compressor excessively increases, an air flow becomes unstable due to blade surfaces of the compressor, leading to surging which may cause self-excited vibration of the air flow. To prevent such surging, therefore, an intake bypass passage is provided to bypass between the upstream part of the intake passage from the compressor and the downstream part of the intake passage from the compressor and an intake bypass valve is provided in this bypass passage so as to open as needed. This can reduce the pressure difference between the inlet and the outlet of the compressor, thereby enabling preventing the occurrence of surging. A supercharger-equipped engine including the above intake bypass passage and intake bypass valve may also be provided with a low-pressure-loop EGR apparatus.
One example of the intake bypass valve of the above type is disclosed in JP-A-2013-83339. This intake bypass valve includes a movable unit having a valve member to open and close a valve seat provided between an in-flow passage and an out-flow passage of the intake bypass passage, on an out-flow passage side, and an elastic member to bias the movable unit in a closing direction, an electromagnetic device to move the movable unit in an opening direction by electromagnetic force against the biasing force of the elastic member, a pressure responsive member provided between a fixed-side member of the electromagnetic device and the movable unit to define a pressure balance chamber partitioned from the out-flow passage, and a pressure introduction passage formed in the movable unit to provide communication between the in-flow passage and the pressure balance chamber. In this intake bypass valve, in a valve closed state where the valve member seats on the valve seat, the air pressure applied to the in-flow passage side of the valve member and the air pressure applied to the pressure balance chamber side are balanced. In the pressure introduction passage, a dynamic pressure reducing member is provided to reduce dynamic pressure of air acting on the pressure balance chamber. With the above configuration, the dynamic pressure reducing member provided in the pressure introduction passage reduces the dynamic pressure of air acting on the pressure balance chamber at the time of start of valve opening. This can shorten a valve opening time and enhance valve opening response.
On the other hand, as a technique provided in a supercharger-equipped engine, a blowby gas recirculation apparatus to return blowby gas generated in the engine to the engine via an intake passage. The above type technique is disclosed in for example JP-A-2009-299645 and JP-A-2012-215155. FIG. 20 is a schematic configuration view showing an engine system including the blowby gas recirculation apparatus disclosed in JP-A-2012-215155. In this engine system, an intake port 2 of an engine 1 is connected to an intake passage 3 and an exhaust port 4 is connected to an exhaust passage 5. An air cleaner 6 is provided at an inlet of the intake passage 3 and a supercharger 7 is provided between the intake passage 3 downstream of the air cleaner 6 and the exhaust passage 5.
The supercharger 7 is arranged to rotate a turbine 9 by exhaust gas flowing in the exhaust passage 5, thereby integrally rotating a compressor 8 via a rotary shaft 10, to increase the pressure of intake air in the intake passage 3. In an exhaust bypass passage 11 provided in the exhaust passage 5 to detour the turbine 9, a waste gate valve 12 is provided with an opening degree adjusted by an actuator 19. When exhaust gas flowing in the exhaust bypass passage 11 is regulated by this valve 12, the rotation speed of the compressor 8 as well as the turbine 9 is adjusted to adjust the supercharging pressure of the supercharger 7. An intercooler 13 is provided in the intake passage 3. A surge tank 3a is provided in the intake passage 3 downstream of the intercooler 13 and a throttle valve 21 is placed in the intake passage 3 upstream of the surge tank 3a. 
An intake bypass passage 41 is provided to bypass between an upstream part of the intake passage 3 from the compressor 8 and a downstream part of the intake passage 3 from compressor 8. In this intake bypass passage 41, an ejector 37 is provided to generate negative pressure by the air flowing in the passage 41. FIG. 21 is a cross sectional view showing a schematic configuration of the ejector 37. This ejector 37 is configured such that the air ejected through a nozzle 37a provided on an air inlet side generates negative pressure in a decompression chamber 37c located between a diffuser 37b provided on an air exit side and the nozzle 37a. Specifically, when air pressure is increased by the compressor 8, a pressure difference occurs between the upstream portion and the downstream part of the intake passage 3 with respect to the compressor 8, thereby generating a pressure difference between the nozzle 37a and the diffuser 37b. This pressure difference causes the air to be ejected from the nozzle 37a to the diffuser 37b, generating the negative pressure in the decompression chamber 37c. 
As shown in FIG. 20, the decompression chamber 37c of the ejector 37 (see FIG. 21) is connected to an outlet of a first blowby gas returning passage 38 to be used during operation (during supercharging) of the supercharger 7. An inlet of the first blowby gas returning passage 38 is connected to a head cover 1b of the engine 1. This passage 38 is arranged to allow the blowby gas leaking from a combustion chamber 16 of the engine 1 into a crank case 1c to return to the combustion chamber 16 through the head cover 1b and the intake passage 3. In each of the head cover 1b and the crank case 1c, blowby gas is accumulated. Accordingly, during supercharging, when negative pressure is generated in the ejector 37, this generated negative pressure acts on the inside of the head cover 1b through the first blowby gas returning passage 38. Thus, the blowby gas is caused to flow from the head cover 1b into the returning passage 38, and then flow to the intake passage 3 upstream of the compressor 8 via the ejector 37 and the intake bypass passage 41. The blowby gas flowing in the intake passage 3 is returned to the combustion chamber 16 via the compressor 8, the intake passage 3 downstream of the compressor 8, and others.
On the other hand, an inlet of a second blowby gas returning passage 39 is connected to the head cover 1b to allow the blowby gas leaking from the combustion chamber 16 to return to the combustion chamber 16 again. An outlet of the second blowby gas returning passage 39 is connected to the surge tank 3a. Further, the head cover 1b is provided with a PCV valve 40 at the inlet of the second blowby gas returning passage 39. Accordingly, during non-supercharging, when negative pressure is generated in the surge tank 3a, this negative pressure acts on the head cover 1b through the second blowby gas returning passage 39. Thus, the blowby gas is caused to flow from the head cover 1b into the returning passage 39 and then flow to the surge tank 3a to return to the combustion chamber 16. The PCV valve 40 is arranged to adjust a flow rate of blowby gas to be introduced from the head cover 1b to the second blowby gas returning passage 39.
To introduce fresh air into the head cover 1b and the crank case 1c, a fresh-air introduction passage 46 is provided between the head cover 1b and the intake passage 3. Furthermore, in the first blowby gas returning passage 38, a check valve 47 is provided to block a flow of gas in an opposite direction to a direction of allowing the blowby gas to flow.
Herein, it is also conceived that the engine system including the supercharger 7 and the blowby gas returning device shown in FIG. 20 is also provided with a low-pressure-loop EGR apparatus. This low-pressure-loop EGR apparatus includes an EGR passage 17 located between the exhaust passage 5 downstream of the turbine 9 and the intake passage 3 upstream of the compressor 8, and an EGR valve 18 provided in the EGR passage 17, as shown by a chain double-dashed line in FIG. 20.